Solutions of polyesters and process for making same



United States Patent SOLUTIONS OF POLYESTERS AND PROCESS FOR MAKING SAMEHobson D. De Witt, New Wilmington, Pa., and Arthur B. Beindorif,Decatur, Ala., assignors to The Chemstrand Corporation, Decatur, Ala., acorporation of Delaware No Drawing. Filed Nov. 5, 1958, Ser. No. 771,942

20 Claims. (Cl. 26030.2)

This invention relates to new compositions of matter and moreparticularly to new and useful compositions of matter comprisingsolutions or dopes of synthetic linear condensation polyesters. It isfurther concerned with new compositions of matter which are capable ofbeing formed into useful articles such as ribbons, films, bristles,fibers, filaments and the like.

Patented Oct. 18, 1960 7 tion polyester compositions in solution whichare stable This application is a continuation-in-part of our 00- pendingapplication Serial No. 608,003, filed September 5, 1956, now abandoned,and entitled Polyester Compositions.

For the sake of simplicity, the present invention will be described asit is applied in the manufacture of fibers and filaments. However, theinvention is not to be limited thereby except insofar as it may belimited by the appended claims.

Various methods are known for converting the polyesters described aboveinto filaments and fibers, such as the so-called melt-spinning,wet-spinning and dry-spinning methods.

Melt-spinning comprises melting chips of a polyester on a heated gridand passing the melt through a filter bed of small particles, such assand, and the like. sequently, the melt is forced through a spinneretand the filaments so formed are cooled. However, meltspinning hascertain disadvantages such as the employment of high temperatures whichmakes the addition of plasticizers and modifying agents diflicult,because there Subis a tendency for the added agents to discolor anddecompose.

In the dry-spinning method the polyester is dissolved in a solventtherefor and extruded through a spinneret in the usual manner. Thesolution is extruded into an atmosphere of inert gas which may beheated. The motion of the inert gaseous atmosphere, the extruded fiberand the application of heat all aid in disposing of the volatilesolvent.

The wet-spinning method in which a solution of polyester is extrudedinto a bath containing a non-solvent for r the polyester has a number ofadvantages over the meltspinning method. For example, the wet-spinningmethod is generally more economical and can be carried out at lowertemperatures. Therefore, plasticizers and other agents may be added witha minimum tendency toward discoloration and decomposition. Furthermore,certain types of plasticizers and modifying agents tend to be lesscompatible for blending in a melt at high temperatures, whereas they canbe readily incorporated in a polyester solution at a low temperature.Solutions offer the further advantage in that they may be easily castinto films or coatings of uniform thickness. This is extremely difficultwith a molten composition because of its relatively high viscosity.

The wet-spinning technique, however, has not been employed commerciallybecause of the lack of suitable solvents. Generally polyesters areinsoluble in the more common organic solvents. From the standpoint oflow cost, solvent power, non-corrosiveness and ease of reand havenon-gelation characteristics.

Another object of the invention is to prepare spinnable solutions ofpolyester compositions.

Other objects and advantages of the invention will be apparent from thefollowing description. 7

The objects of the invention are in general accomplished by dissolvingthe synthetic linear condensation polyesters in a solvent having thegeneral formula wherein R is oxygen, sulfur or an amine (=NH) radicaland R is hydrogen or methyl and wherein there'may be from l-3 methylgroups attached to the carbon atoms of the ring; or a solvent having thegeneral formula (I N J R wherein R is oxygen, sulfur or an amine (=NH)radical. Among the compounds having the general Formulae I and II areoxazole, thiazole, irnidazole, 4-methyloxazole, S-methyloxazole,4-methylthiazole, S-methylthiaizole, 4- methylimidazole,S-methylimidazole, 4,5-dimethyloxazole, 4,5-dimethylthiazole,4,5-dimethylimidazole, 2,'4,5 -'t-rimethyloxazole,2,4,5-trimethylthiazole, 2,4,5-trimethylimidazole, benzoxazole,benzothiazole and :benzimidazole.

Solutions of high solids content and good stability can be prepared bymixing the polyester in the compounds mentioned hereinabove and heatingto a temperature in the range of C. to the boiling point of the mixture.If desired, the mixture may be stirred while heating. However, stirringis not necessary to effect solution, although it has been found that thepolyester goes into solution more smoothly and evenly and with a greaterrate of speed when stirring is employed. Whether stirring is employed ornot, a miscible mixture of the synthetic linear condensation polyesteris attained.

The maximum solids concentration of the polyester that can be obtainedin the solution and the viscosity of the solution depend upon the natureof the polyester, the solvent and the temperature In the manufacture offilaments and fibers, a polyester having a molecular weight of at least10,000 is employed'in making the solution. Lower molecular weightpolyesters may be utilized when the solution to be formed is to beusedas a coating or as a lacquer. In preparing solutions ordopes-suitable for spinning into filaments and fibers, 10 to 25 percentby weight of the polyester, based on the total weight of the solution,is suitable. While it is preferred to employ 10 to 25 percent by Weight,based on the total weight of the solution, of the polyester in thesolvent when the solution is to be used for the preparation of fibersand filaments, it is to be understood that as little as 5 percent orless and as much as 30 percent or more of the polyester may be utilizedwhen the solution is .to be employed for other purposes, such ascoatings and lacquers and the like, or when lower or higher molecularweight polyesters are to be dissolved in the new solvents of thisinvention. The amount of any specific polyester which can be dissolvedin solvents of this invention will be readily evident to those skilledin the art- The synthetic linear condensation polyesters contemplated inthe practice of the invention are those formed from dicarboxylic acidsand glycols, and copolyesters or modifications of these polyesters andcopolyesters. In a highly polymerized condition, thesepolyesters and.copolyesters can be formed into filaments and the like, andsubsequently oriented permanently by cold drawing. The polyesters andcopolyesters specifically useful in the instant invention arethoseresulting from heating one or more of the glycols of the seriesHO(CH -OH, in which n is an integer from '2 .to 10, with one or moredicarboxylic acids or ester-forming derivatives thereof. Among thedicarboxylic acids and ester-forming deriva tives thereof useful in thepresent invention there may be named terephthalic acid, isophthalicacid, sebacic acid, adipic acid, p-carboxyphenoacetic acid, succinicacid, p,p'- dicarboxybiphenyl, p,p'dicarboxycarbanilide,p,p'dicarboxythiocarbanilide, p,p-dicarboxydiphenylsulfone,.p-carboxyphenoxyacetic acid, p-carboxyphenoxypropionic acid,p-carboxyphenoxybutric acid, p-carboxyphenoxyvaleric acid,p-carboxyphenoxyhexanoic acid, p-carboxphenoxy heptanoic acid,p,p'-dicarboxydiphenylmethane, p,p'-dicarboxydiphenylethane, p,pdicarboxydiphenylpropane, p,p-dicarboxydiphenylbutane,p,p'-dicarboxydiphenylpentane, p,p'-dicarboxydiphenylhexane,p,p-dicarboxydiphenylheptane, p,p'-dicarboxydiphenyloctane,p,p-dicarboxydiphenoxyethane, p,p'-dicarboxydiphenoxypropane,p,p-dicarboxydiphenoxybutane, p,p-dicarboxydiphenoxypentane,p,p'-dicarboxydiphenoxyhexane, 3-alkyl 4-(betacarboxy ethoxy)benzoicacid, oxalic acid, glutaric acid, pimelic acid, suberic acid, azelaicacid and the dioxy acids of ethylene dioxide having the general formula,

wherein n is an integer from 1 to 4, and the aliphatic andcycloaliphatic aryl esters and half esters, ammonium and amine salts,and the acid halides of the above-named compounds and the like. Examplesof the glycols which may be employed in practicing the instant inventionare ethylene glycol, trimethylene glycol, tetramethylene gycol anddecamethylene glycol, etc. Polyethylene terephthalate, however, ispreferred because of the ready availability of terephthalic acid andethylene glycol, from which it is made. It also has a relativelyhighmelting .point of about 250 through 255 C. and this property isparticularly desirable in the manufacture of filaments in the textileindustry.

Among the modified polyesters and copolyesters which are useful in thepractice of the instant invention are the polyesters and copolyestersmentioned above modified with chain terminating groups havinghydrophilic properties, such as the monofunctional ester-formingpolyethers bearin g the general formula,

'(III) RO-'[ 2)m ]x( 2)n wherein R is an alkyl group containing 1 to 18carbon atoms or an aryl group containing 6 to 10 carbon atoms,

and m and n are integers from 2 to 22, and x is a whole numberindicative of the degree of polymerization, that is, x 1s an integerfrom 1 to 100 or greater. Examples of such compounds aremethoxypolyethylene glycol, ethoxypolyethylene glycol,n-propoxypolyethylene glycol, isopropoxypolyethylene glycol,butoxypolyethylene glycol, phenoxypolyethylene glycol,methoxypolypropylene glycol, methoxypolybutylene gycol,phenoxypolypropylene glycol, phenoxypolybutylene glycol,methoxypolymethy-lene glycol, and the like. Suitable polyalkylvinylethers having one terminal hydroxyl group are the addition polymersprepared by the homopolymerization of alkylvinyl ethers wherein thealkyl group contains from l'to 4 carbon atoms. Examples of suchchain-terminating agents'are hydroxy polymethylvinyl ether, hydroxypolyethylvinyl ether, hydroxy polypropylvinyl ether,hydroxypolybutylvinyl ether, hydroxy polyisobutylvinyl ether and thelike. The chain-terminating agents or compounds may be e ployed in thepreparation of the modified polyesters in amounts ranging from 0.05 molpercent to 4.0 mol percent, based on the amount of dicarboxylic acid ordialkyl ester thereof employed in the reaction mixture. It is to benoted that when chain-terminating agents are employed alone, i.e.,without a chain-branching agent, the maximum amount that can be employedin the reaction mixture is 1.0 mol percent. Thus, unexpectedly, theaddition of controlled amounts of chain-branching agents along with thechain-terminating agents allows the introduction of an increased amountof the latter into the polymer chain than is otherwise possible whenemploying the chainterminating agents alone.

One will readily appreciate that the weight percent of chain-terminatingagent which may be employed in this invention will vary with themolecular weight of the agent. The range of average molecular weights ofthe chain-terminating agents suitable for use in this invention is from500 to 5000, with those agents having a molecular weight in the range of1000 to 35 0O being-preferred.

Materials suitable as chain-branching agents or crosslinking agents,which are employed to increase the viscosity or molecular weight of thepolyesters, are the polyols which have a functionality greater than two,that is, they contain more than two functional groups, such as hydroxyl.Examples of suitable compounds are pentaerythritol; compounds having theformula:

wherein 'R is an alkylene group containing from '3 to 6 carbon atoms andn is 'an integer from 3 to -6, for example, glycerol, sorbitol, hexanetriol-1,2,6, and the like; compounds having the formula:

wherein R is an alkylene group containing from 2 to 6 carbon atoms, forexample, trimethylol ethane, trimethylol propane, and like compounds upto trimethylol hexane; and the compounds having the formula (0 H9110 Hawherein n is an integer from 1 to 6. As examples of compounds having theabove formula there may be named trimethylol benzene-1,3,5, triethylolbenzene-1,3,5, tripropylol benzene-1,3,5, tributylol benzene-1,3,5,.etc.

Aromatic polyfunctional acid esters may also be employed in thisinvention as chain-branching agents and particularly those having theformula:

and in which R, R and R" are .alkyl groups containing 1 to 3 carbonatoms and R' is hydrogen or alkyl groups having 1 to 2 carbon atoms. Asexamples of compounds having the above formula there may benamedtrimethyl trimesate, tetramethyl pyromellitate, tetramethylmellophonate, trimethyl hemimelitate, trimethyl trimellitate,tetramethyl prehnitate, and the like. In addition, there may be employedmixtures of the above esters which are obtained in practical synthesis.That is, in most instances when preparing any of the compounds.havingthe above formula, other related compounds having the sameformula may be present in small arnounts as impurities. This does notaffect the .compound as a chainbranching agentin the preparation of themodified polyesters and copolyesters described herein.

The chain-branching agents or cross-linking agents may be employed inthe preparation of the polyesters and copolyesters in amounts rangingfrom 0.05 mol percent to 2.4 mol percent, based on the amount ofdicarboxylic acid or dialkyl ester thereof employed in the reactionmixture. The preferred range of chain-branching agent :for use in thepresent invention is from 0.1 to 1.0 mol percent.

In the practice of the present invention, the calculated amounts ofchainaterminating agent or chain-terminating agent and chain-branchingagent or cross-linking agent are charged to the reaction vessel at thebeginning of the first stage of the esterification reaction and thereaction proceeds as in any well-known esterification polymerization.The first step or stage of the reaction is carried out at atmosphericpressure and at a temperature in the range of 90 C. to 250 C. andpreferably between 150 C. and 220 C. when trom 0.001 to 1.0 percent byweight, based on the weight of the .dicarboxylic acid or ester thereof,of a suitable esterification catalyst, such as manganous formate or zincacetylacetonate, is employed. If desired, the reaction may be carriedout at pressures above or below atmospheric. Methanol is evolved whichis continuously removed by distillation. At the completion of the firststage, the excess glycol, if any, is distilled all prior to entering thesecond stage of the reaction.

In the second or polymerization stage, the reaction is conducted atreduced pressures and preferably in the presence of an inert gas, suchas nitrogen, in order to prevent oxidation. This can be accomplished bymaintaining a nitrogen blanket over the reactants, said nitrogencontaining less than 0.003 percent oxygen. For optimum results, apressure within the range of less than 1 mm. up to 5 mm. of mercury isemployed. This reduced pressure is necessary to remove the free ethyleneglycol that is formed during this stage of the reaction, the ethyleneglycol being volatilized under these conditions and removed from thesystem. The polymerization step is conducted at a temperature in therange of 220 to 300 C. This stage of the reaction may be effected eitherin the liquid, melt or solid phase. In the liquid phase, particularly,reduced pressures must be employed in order to remove the free ethyleneglycol which emerges from the polymer as a result of the condensationreaction.

In the preparation of the described polyesters, the first stage of thereaction'takes place'in approximately to 2 hours, when employing asuitable esterification catalyst. In the absence of a catalyst, times upto 6 hours may be necessary in order to complete this phase of thereaction. In the second stage, a reaction time of approximately 1 to 4hours may be employed with a time of 1 to 3 hours being the optimum,depending on catalyst concentration, temperature, viscosity desired,amount of color allowable in the finished polymer, etc.

The modified linear condensation polyesters, produced in accordance withthe present invention, have a specific viscosity in the range of 0.30 to0.60, which represents the fiberand filament-forming polymers. It is tobe understood, o-f course, that non-fiber-forming polyesters may beproduced by means of the present invention, which have a specificviscosity greater or less than that reiterated above and such polyestersare useful, for example, in the manufacture of coating compositions,lacquers, molding compositions, and the like. This specific viscosityrange and variations thereof also are applicable to the unmodifiedpolyesters, such as polyethylene terephthalate. The specific viscosityrange of the fiber-forming polymers, that is, from 0.3 to about 0.6,indicates high molecular weight polymers of from about 10,000 to about50,000 molecular weight.

If it is desired to produce shaped articles from the polyester solutionsof the present invention which have a modified appearance or modifiedproperties, various agents to accomplish these effects may be added tothe 6 polyester solutions of this invention prior to the fabrication ofthe articles without any ill effects thereon. Such added agents might beplasticizers, pigments, dyes, antistatic agents, fire-retarding agents,etc.

The following examples are intended to illustrate the new compositionsof the invention more fiully, but are not intended to limit the scope ofthe invention, for it is possible to eifect many modifications therein.In the examples, all parts and percents are by weight unless otherwiseindicated.

Example I 9 grams of benzothiazole and 1 gram of polyethyleneterephthalate were mixed together and warmed with stirring to 150 C.where the polymer readily dissolved,

yielding a clear fluid solution suitable for both wet or' dry spinning.On cooling, the solution became hazy at 110 C. and solidified at 100 C.,but was easily redissolved upon the application of heat.

Example II There was charged to a reaction vessel 82 grams of dimethylterephthalate, 106.2 grams of ethylene glycol (approximately 88 ml.) and8.2 grams of ethoxypolyethylene glycol having an average molecularweight of about 3050 (0.5 mol percent based on the mols of dimethylterephthalate). Subsequently, 40 mg. of manganous formate was added tothe reaction vessel. The reactants were well mixed and heated at 177 C.until solution was effected. The mixture was maintained at thistemperature for 90 minutes to bring about the ester-interchangereaction. Thereatter, the temperature was raised to 225 C. to removeexcess ethylene glycol and maintained at this temperature under a vacuumof less than 1 mm. of mercury for 3 hours to eifect polymerization.There was obtained a high molecular weight polyester having a meltingpoint of about 255 C. and a specific viscosity of about 0.3 at 25 C.calcuated in a 2 to 1 mixture of phenol-trichloro phenol containing 0.5percent by weight of the polymer. 9 grams of hemethiazoleiand 1 gram ofthe polyester so prepared were mixed together and warmed with stirringto 150 C. where the polymer readily dissolved, yielding a clear fluidsolution suitable for both wet and dry spinning.

On cooling, the solution became hazy at 110 C. and

solidified at C. but was easily redissolved upon the application ofheat. 7

Example III at C. and solidified at 95 C. but was easilyv redissolvedupon the application of heat. The solution was suitable for theformation of fibers by either the Wet or dry spinning method.

Example IV 8 grams of benzothiazole and 2 grams of polyethylene ExampleV 8 grams of benzothia-zole and 2 grams of the polyester, prepared bythe process set forth in Example II, were mixed together and warmed withstirring to C."

where the polymer readily dissolved, yielding a clear fluid solutionsuitable for either wet or dry spinningr On cooling, the solution becamehazy- 7 On cooling, the solution became solid at 120 C. but was easilyredissolved upon the application of heat.

Example VI 9 grams of benzoxazole and 1 gram of polyethyleneterephthalate were mixed together and warmed with stirring to 135 C.where the polymer readily dissolved, yielding a clear fluid solutionsuitable for both wet or dry spinning. On cooling, the solutionsolidified at 105 C. but was easily redissolved upon the application ofheat.

Example VII 9 grams of benzoxazole and 1 gram of the polyester, preparedaccording to the procedure of Example II, were mixed together and warmedwith stirring to 135 C. where the polymer readily dissolved, yielding aclear fluid solu tion suitable for either wet or dry spinning. Oncooling, the solution solidified at 135 C. but was easily redissolvedupon the application of heat.

Example VIII 9 grams of benzoxazole and 1 gram of the polyester employedin Example III were mixed together and warmed with stirring to 135 C.where the polymer readily dissolved, yielding a clear fluid solutionsuitable for either wet or dry spinning. On cooling, the solutionsolidified at 100 C. but was easily redissolved upon the application ofheat.

Example IX 8 grams of benzoxazole and 2 grams of the polyester employedin Example III were mixed together and warmed with stirring to 150 C.where the polymer readily dissolved, yielding a clear fluid solutionsuitable for either wet or dry spinning. On cooling, the solutionsolidified at 125 C. but was easily redissolved upon the application ofheat.

Example X 9 grams of imidazole and 1 gram of polyethylene terephthalatewere mixed together and warmed with stirring to 160 C. where the polymerreadily dissolved, yielding a clear fluid solution suitable for both wetor dry spinning. On cooling, the solution became hazy at 110 C. andbegan to solidify at 85 C. but was easily redissolved upon theapplication of heat.

Example XI Example XII 9 grams of imidazole and 1 gram of the modifiedpolyester employed in Example III were mixed together and warmed withstirring to 160 C. where the polymer readily dissolved, yielding a clearfluid solution, suitable for both wet and dry spinning. Upon cooling,the solution became hazy at 105 C. and began to solidify at 80 C. butwas easily redissolved upon the application of heat.

Example XIII 8 grams of imidazole and 2 grams of polyethyleneterephthalate were mixed together and warmed with stirring to 150 C.where the polymer readily dissolved, yielding a clear fluid solutionsuitable for both wet and dry spinning. On cooling, the solutionsolidified at 130 1(1). but was, easily redissolved upon the applicationof 8 Example XIV 8 grams of benzimidazole and 2 grams of polyethyleneterephthalate were mixed together and warmed with stirring to 180 C.where the polymer readily dissolved, yielding a clear fluid solutionsuitable for both wet or dry spinning. On cooling, the solution began tosolidify at 160 C. but was easily redissolved upon the application ofheat.

Example XV There was charged to a reaction vessel 1650 grams of dimethylterephthalate, 1980 grams (approximately 1775 ml.) of ethylene glycoland 165 grams of methoxypolyethylene glycol having an average molecularweight of about 200-0 (1.0 molpercent based on the mols of dimethylterephthalate). There was also added to the reaction vessel l.32 gramsofpentaerythritol. Subsequently, 1.07 grams of zinc acetylacetonate wereadded to the reaction vessel. The reactants were well mixed and heatedfor about minutes at atmospheric pressure and at a temperature graduallyraised from 155 C. to 198 C. until solution was effected. During thistime methyl alcohol which was formed in the reaction was removed bydistillation. Subsequently, the reactants were heated for about 45minutes under atmospheric pressure at a temperature which was graduallyraised from 198 C. to 240 C. to remove excess ethylene glycol. Then thetemperaturewas raised from 240 C. to about 280 C. over a period of about5 minutes while the pressure was gradually decreased from atmosphericpressure to about 1 mm. of mercury. The reaction mixture was subjectedfor about 1% hours to 280 C. and aboutl mm. of mercury to effectpolymerization. There was obtained a highmolecular weight polyesterhaving a melting point of about 255 C. and a specific viscosity of 0.50at 25 C. calculated in a 2 to 1 mixture of phenol-trichlorophenolcontaining 0.5 percent by weight of polymer. 0.5 gram of the polyesterso prepared and 9.5 grams of benzoxazole were mixed together and heatedwith stirring. The polymer dissolved rapidly at about 160 C. to 170 C.On cooling, the solution became slightly turbid around C. andprecipitation of the polymer began to occur at about 105 C. The solutionbecame semi-solid at 100 C. The solution so obtained was clear, slightlyviscous and suitable for the preparation of coating.

Example XVI Example XVII 3 grams of the polyester prepared in accordancewith the procedure of Example XV and 7 grams of benzoxazole were mixedtogether and heated with stirring to about 165 C. where the polymerdissolved with some difficulty. Precipitation of the polyester from thesolution began to occur at about C. to about C. At 150 C. the polyesterprecipitated from the solution. However, the solution was clear, viscousand suitable for the casting of films at temperatures of C. or above.

The polyester compositions of this invention can be usefiully employedin various manners, for example, in the coating field where it may bedesirable to coat textile fabrics. Thus, fabrics can be coated and/ orimpregnated with the polyester solutions herein described and thentreated, that is soaked, in a non-solvent for the polyester in order toprecipitate the polyester in and on the fabric.

9 Metals, paper and impervious films may also-be coated with thepolyester compositions of this invention'by conventional and well-knownprocedures.

One of the principal advantages, of the instant invention is that itprovides polyester compositions which are readily convertible to usefulshaped articles by the wet or dry spinning methods which are moreeconomical than the melt-spinning method. Numerous other advantages ofthis invention will be readily apparent to those skilled in the art fromreading the instant description.

As many aparently widely different embodiments of this invention may bemade without departing from the "spirit and scope thereof, it is tobeunderstood that the same is not to be limited to the specificembodiments thereof, except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a solution of a syntheticlinear condensation polyester dissolved in a solvent selected from thegroup consisting of compounds having the formula:

wherein R is selected from the group consisting of oxygen, sulfur and=NH and R is selected from the group consisting of hydrogen and -CH andwherein there are from 1 to 3 methyl groups attached to the carbon atomsofthe ring; and compounds having the formula:

N l R wherein R is selected from the group consisting of oxygen, sulfurand =NH; said polyester being selected from the group consisting of (A)polyesters formed by the reaction of at least one dicarboxylic acidselected from the group consisting of aromatic dicarboxylic acids andaliphatic dicarboxylic acids and at least one glycol of the series HO(CHOH wherein n is an integer from 2 to 10, (B) the polyesters of (A)modified by 0.05 mol percent to 1.0 mol percent, based on the totalweight of said dicarboxylic acid, of a chain terminator selected fromthe group consisting of polyalkylvinyl ethers having one terminalhydroxyl group wherein the alkyl group contains 1 to 4 carbon atoms, andcompounds having the formula:

wherein R is selected from the group consisting of alkyl groupscontaining 1 to 18 carbon atoms and aryl groups containing 6 to 10carbon atoms, m and n are integers from 2 to 22, and x is an integerfrom 1 to 100, indicative of the degree of polymerization, and (C) thepolyesters of (B) containing 0.05 mol percent to 4.0 mol percent basedon the total weight of said dicarboxylic acid modified by 0.05 molpercent to 2.4 mol percent based on the total weight of saiddicarboxylic acid, of a chainbranching agent selected from the groupconsisting of pentaerythritol, compounds having the formula:

wherein R is an alkylene group containing from 3 to 6 carbon atoms and nis an integer from 3 to 6, and compounds having the formula:

wherein R is an alkylene group containing from 2 to 6 carbons atoms,compounds having the formula:

(CHzhOH! '10 wherein n is an integer from 1 to 6, and compounds havingthe formula:

wherein R, R' and R" are alkyl groups containing 1 to 3 carbon atoms andR is selected from the group consisting of hydrogen, methyl and ethylradicals.

2. A new composition of matter :as defined in claim 1 wherein thepolyester is polyethylene terephthalate.

3. A new composition of matter as defined in claim 1 wherein the solventis benzothiazole.

4. Anew composition of matter as defined in claim 1 wherein the solventis benzoaxazole.

5. A new composition of mater as defined in claim 1 wherein the solventis imidazole.

6. A new composition of matter as defined in claim 1 wherein the solventis benzimidazole.

7. A new composition of matter as defined in claim 1 wherein the solventis thiazole.

8. A new composition of matter as defined in claim 1 wherein the chainterminator is ethoxypolyethylene glycol.

9. A new composition of matter as defined in claim 1 wherein the chainterminator is hydroxy polyvinylmethyl ether.

10. A new composition of matter as defined in claim 1 wherein the chainterminator is methoxypolyethylene v glycol.

11. A new composition of matter as defined in claim 1 wherein the chainterminator is n-propoxypolyethylene glycol.

12. A new composition of matter as defined in claim 1 wherein thecross-linking agent is trimethyl trimesate.

13. A new composition of matter as defined in claim 1 wherein thecross-linking agent is pentaerythritol.

14. A new composition of matter as defined in claim 1 wherein thecross-linking agent is tripropyl trimesate.

15. A new composition of matter as defined in claim 1 wherein thecross-linking agent is sorbitol.

16. A new fiber-forming composition of matter comprising a misciblemixture containing 10 to 25 percent, based on the total weight of themixture, of polyethylene terephthalate having a molecular weight of atleast 10,000 and a solvent selected from the group of compounds havingthe general formula:

wherein R is selected from the group consisting of oxygen sulfur and anamine (=NH) radical and R is selected from the group consisting ofhydrogen and methyl and wherein there are from 1-3 methyl groupsattached to the carbon atoms of the ring; and

i J R wherein R is selected from the group consisting of oxygen, sulfurand an amine (=NH) radical.

17. A process for preparing a new composition of matter comprisingmixing a synthetic linear condensation polyester with a solvent selectedfrom the group consisting of compounds having the formula:

( N 'i'l wherein R is selected from the group consisting of oxygen,sulfur and =NH and R is selected from the group con- [FI R) wherein R isselected from the group consisting of oxygen, sulfur and :NH; saidpolyester being selected from the group consisting of (A) polyestersformed by the reaction of at least one dicarboxylic acid selected fromthe group consisting of aromatic dicarboxylic acids and aliphaticdicarboxylic acids and at least one glycol of the series HO(CH OHwherein n is an integer from 2 to 10, (B) the polyesters of (A) modifiedby 0.05 mol percent to 1.0 mol percent, based on the total weight ofsaid dicarboxylic acid, of a chain terminator selected from the groupconsisting of polyalkylvinyl ethers having one terminal hydroxyl groupwherein the alkyl group contains 1 to 4 carbon atoms, and compoundshaving the formula:

wherein R is selected fromthe group consisting of alkyl groupscontaining 1 to 18 carbon atoms and aryl groups containing 6 to 10carbon atoms, "m and n are integers from 2 to 22, and x is an integerfrom 1 to 100, indicative of the degree of polymerization, and (C) thepolyesters of (B) containing 0.05 mol percent to 4.0 mol percent basedon the total weight of said dicarboxylic acid modified by 0.05 molpercent to 2.4 mol percent based on the total weight of saiddicarboxylic acid, of a chain-branching agent selected from the groupconsisting of pentaerythritol, compounds having the formula:

wherein Ris an alkylene group containing from 3 to 6 carbon atoms and nis an integer from 3 to 6, and compounds having the formula:

wherein R is an alkylene group containing from 2 to 6 carbon atoms,compounds having the formula:

wherein n is an integer from 1 to 6, and compounds havingthe formula:

wherein R, R and R" are alkyl groups containing 1 to 3 carbon atoms andR' is selected from the group consisting of hydrogen, methyl and ethylradicals, and heating the mixture to a temperature in the range of C. tothe boiling point of the mixture.

18. The process as defined in claim 17 wherein the solvent isbenzothiazole. I

19. The process as defined in claim 17 wherein the solvent isbenzoxazole.

20. The process as defined in claim 17 wherein the solvent is imidazole.

No references cited.

1. A NEW COMPOSITION OF MATTER COMPRISING A SOLUTION OF A SYNTHETICLINEAR CONDENSATION POLYESTER DISSOLVED IN A SOLVENT SELECTED FROM THEGROUP CONSISTING OF COMPOUNDS HAVING THE FORMULA: